全文获取类型
收费全文 | 3762篇 |
免费 | 634篇 |
国内免费 | 534篇 |
专业分类
化学 | 2940篇 |
晶体学 | 40篇 |
力学 | 189篇 |
综合类 | 42篇 |
数学 | 459篇 |
物理学 | 1260篇 |
出版年
2024年 | 12篇 |
2023年 | 68篇 |
2022年 | 136篇 |
2021年 | 130篇 |
2020年 | 150篇 |
2019年 | 151篇 |
2018年 | 143篇 |
2017年 | 117篇 |
2016年 | 154篇 |
2015年 | 172篇 |
2014年 | 188篇 |
2013年 | 251篇 |
2012年 | 300篇 |
2011年 | 332篇 |
2010年 | 227篇 |
2009年 | 204篇 |
2008年 | 276篇 |
2007年 | 188篇 |
2006年 | 184篇 |
2005年 | 183篇 |
2004年 | 154篇 |
2003年 | 154篇 |
2002年 | 185篇 |
2001年 | 153篇 |
2000年 | 108篇 |
1999年 | 85篇 |
1998年 | 72篇 |
1997年 | 44篇 |
1996年 | 90篇 |
1995年 | 64篇 |
1994年 | 46篇 |
1993年 | 29篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 28篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1974年 | 1篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有4930条查询结果,搜索用时 15 毫秒
181.
Ho Van Doanh Phan Bao Quoc Hieu Pham Ngoc Son Dao Van Hoang Tam Hoang Duc Ho Manh Dung 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(3):1361-1365
Journal of Radioanalytical and Nuclear Chemistry - To keep the accredited category for the gamma spectrometry test in our laboratory, the efficiency curves of a HPGe detector for soil sample in... 相似文献
182.
David M. Koshy Dr. Shucheng Chen Dr. Dong Un Lee Dr. Michaela Burke Stevens Ahmed M. Abdellah Samuel M. Dull Gan Chen Dr. Dennis Nordlund Dr. Alessandro Gallo Dr. Christopher Hahn Dr. Drew C. Higgins Dr. Zhenan Bao Dr. Thomas F. Jaramillo 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(10):4072-4079
Ni,N-doped carbon catalysts have shown promising catalytic performance for CO2 electroreduction (CO2R) to CO; this activity has often been attributed to the presence of nitrogen-coordinated, single Ni atom active sites. However, experimentally confirming Ni−N bonding and correlating CO2 reduction (CO2R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile-derived Ni,N-doped carbon electrocatalysts (Ni-PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO2R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X-ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square-planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts. 相似文献
183.
One‐Pot Synthesis of Pomegranate‐Structured Fe3O4/Carbon Nanospheres‐Doped Graphene Aerogel for High‐Rate Lithium Ion Batteries
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Dafang He Lixian Li Fengjuan Bai Chenyang Zha Prof. Liming Shen Prof. Harold H. Kung Prof. Ningzhong Bao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(13):4454-4459
A unique hierarchically nanostructured composite of iron oxide/carbon (Fe3O4/C) nanospheres‐doped three‐dimensional (3D) graphene aerogel has been fabricated by a one‐pot hydrothermal strategy. In this novel nanostructured composite aerogel, uniform Fe3O4 nanocrystals (5–10 nm) are individually embedded in carbon nanospheres (ca. 50 nm) forming a pomegranate‐like structure. The carbon matrix suppresses the aggregation of Fe3O4 nanocrystals, avoids direct exposure of the encapsulated Fe3O4 to the electrolyte, and buffers the volume expansion. Meanwhile, the interconnected 3D graphene aerogel further serves to reinforce the structure of the Fe3O4/C nanospheres and enhances the electrical conductivity of the overall electrode. Therefore, the carbon matrix and the interconnected graphene network entrap the Fe3O4 nanocrystals such that their electrochemical function is retained even after fracture. This novel hierarchical aerogel structure delivers a long‐term stability of 634 mA h g?1 over 1000 cycles at a high current density of 6 A g?1 (7 C), and an excellent rate capability of 413 mA h g?1 at 10 A g?1 (11 C), thus exhibiting great potential as an anode composite structure for durable high‐rate lithium‐ion batteries. 相似文献
184.
185.
Promoted by SmI3 cycloalkanone trimethylsilyl enol ethers were reacted with aldehydes to give α,α′-bis (substituted-benzylidene) cycloalkanones. 相似文献
186.
Imines can be readily allylated with samarium/allyl bromide system to afford homoallylamines in satisfactory yields in THF under mild conditions. 相似文献
187.
188.
189.
Fuzzy Optimization and Decision Making - Data envelopment analysis (DEA) is a classical and prevailing tool for estimating relative efficiencies of multiple decision making units (DMUs). However,... 相似文献
190.